Hydraulically operated percussive mechanisms are used in mounted implements, such as for example hydraulic hammers or drilling hammers, wherein the mounted implements are mounted on carrier vehicles, in particular mobile excavators, and are connected to the hydraulic system thereof via a pressure line and a return line. Percussive mechanisms have a percussive piston which has one or more hydraulic drive surfaces, at least one of which is, by way of a valve, connected alternately to a return line, which is at low pressure, to the tank of the carrier vehicle or via a pressure line, which is at high pressure, to the pump of the mounted implement, such that the percussive piston performs an oscillating movement along its longitudinal axis. During normal operation, at the end of its movement in one movement direction, the percussive piston strikes a tool, wherein the tool is a chisel, an adapter for piledriving or pipe driving, or an anvil arranged between the percussive piston and the tool.
Hydraulically operated percussive mechanisms have, in some cases, a pressure accumulator in the form of a piston accumulator in order to store kinetic energy of the percussive piston. The upper, cylindrical end, situated opposite the tool, of the percussive piston projects into a gas-filled gas space of the pressure accumulator, wherein a seal which bears against the end of the piston prevents an escape of the gas along the percussive piston.
As the piston moves in the direction of the gas space during the return stroke, the end of the piston displaces gas within the gas space, which thus decreases in size, leading to an increase in the gas pressure. The compressed gas exerts a force on the end of the piston, said force increasing as the gas volume decreases in size. Said force is utilized to accelerate the piston in the direction of movement toward the tool.
During operation, there are thus three characteristic piston positions which can be associated with a respective gas pressure. For example, if a hydraulic hammer which has a percussive mechanism is raised or set down horizontally, its percussive piston is situated in the lower rest position, in which the gas pressure in the piston accumulator assumes its lowest value. When the processing of a piece of material using a hydraulic hammer is ended and the operation of the percussive mechanism is stopped, in order to position the hydraulic hammer differently, the percussive piston assumes its rest position. If the chisel is pressed with its tip against material, the chisel is pushed into the housing of the percussive mechanism until it comes to rest against a stop. In this case, the percussive mechanism is pushed in the upward return stroke direction, in the direction of the gas space, and assumes the impact position, wherein the gas pressure in the piston accumulator assumes a value higher than that in the rest position. When the percussive mechanism is activated, the percussive piston is then hydraulically moved further in the return stroke direction until it reaches its upper reversal point, at which the gas pressure assumes its highest value, wherein the position at the upper reversal point is dependent on the usage conditions of the percussive mechanism and the operating pressure and the pressure in the piston accumulator, and may therefore vary.
Owing to leakage along the seals and gas flows through the seal or the diaphragm or bubble diffusion, the gas pressure falls over the course of time. To maintain the effectiveness of the accumulator, it is thus necessary for the fill pressure in the accumulator to be checked at regular intervals and for the accumulator to be replenished with gas if required. For checking the gas pressure, fittings are necessary for the connection of a pressure measurement implement, for example a manometer, to the gas space. Such fittings comprise a hose and a manometer and, for filling and release purposes, also discharge and filling valves, a pressure reduction valve and screw connections in order for the fittings to be connected to a gas storage bottle. On the gas space, there is provided a shut-off valve or a mechanically opening check valve, to which the fittings are connected, and in addition, normally also a sealing closure screw for preventing an undesired escape of gas.
Since, during the operation of the percussive mechanism, the gas pressure in the piston accumulator constantly changes in a manner dependent on the position of the percussive piston, the gas pressure in the piston accumulator must be measured when the percussive piston is in a particular and defined position, which is possible only when the percussive mechanism is deactivated, that is to say when the hydraulic system is unpressurized. To measure the gas pressure, the rest position of the percussive piston is used, as the percussive piston is situated in a geometrically defined position, specifically at the lower stop.
The checking of the gas pressure is time-consuming because, before the measurement, components such as closure screws must be released, screw connections must be made and, after the measurement, the connection must be released again and the closure screw screwed in again.
Failure to carry out regular checks of the gas pressure can result in a drop in the gas pressure, which reduces the effectiveness of the accumulator and impairs the performance of the percussive mechanism and, for example as a result of excessively intense pressure fluctuations, can also lead to damage of components. The fittings and equipment for the checking of the gas pressure must be available for the checking of the gas pressure and must be operational, and the user must be familiar with the use of the fittings.
JP 2008114296 has disclosed a gas pressure indicator device which is arranged on the hydraulic chamber and in the case of which the gas pressure of the pressure accumulator acts directly on a spring-loaded piston which, with increasing gas pressure, is displaced in the direction of the spring. If the piston is displaced, a bar which is connected fixedly in terms of motion to the piston protrudes out of the housing of the indicator and reveals one or more marks, for example in the form of a groove. The higher the gas pressure acting on the piston, the further the piston is displaced, and the further the bar protrudes out of the housing. During the filling of the accumulator, the marking indicates a particular gas pressure. After measurement has been performed, by virtue of a cap being screwed onto the housing of the device, the bar and the piston are pushed in again counter to the pressure of the gas, in order that the piston and the bar do not permanently move owing to the fluctuating gas pressure during operation. To activate the indicator device, the cap must be removed again.
Percussive mechanisms may furthermore have pressure accumulators in the form of a hydraulic accumulator for the purpose of storing pressurized oil of the hydraulic system. The gas space of a hydraulic accumulator is separated from an oil space by way of a separating element in the form of a piston, an elastic diaphragm or an elastic, hose-like or pot-shaped bladder. The oil space is connected to the hydraulic system directly or via a throttle or a valve. In order to check the gas pressure or for filling purposes or in order to release the gas charge, corresponding fittings such as manometers, hoses and pressurized gas bottles can be connected by way of a valve which is connected to the accumulator space. If, in the hydraulic system, an operating pressure prevails which is higher than the fill pressure within the gas space, oil flows into the oil space and displaces the separating element in the direction of the gas space, whereby the oil space is increased in size, the gas space is reduced in size and the gas is compressed, to a pressure corresponding to the pressure of the oil. Thus, when the oil demand of the consumer is low, the oil that is delivered by the pump can be stored in the hydraulic accumulator in order to reduce the pressure increase in the hydraulic system, and when the demand of the consumer is high, oil can be released from said hydraulic accumulator in order to reduce the pressure drop in the hydraulic system. Intense pressure fluctuations and pressure peaks are thus avoided.
In the case of known indicator devices, it has proven to be disadvantageous that the indicator device must firstly be activated by a user by the removal of the cap, such that there is the risk that the user, in failing to adhere to the service intervals, neglects to perform such activation and the percussive mechanism is operated with an excessively low gas fill pressure, whereby the performance of the percussive mechanism is reduced and components are possibly damaged.
Even if the indicator device were always activated by virtue of the cap being left off, and wear of the indicator device were accepted, it would be the case even in the presence of an excessively low gas fill pressure that, during operation, the gas pressure would repeatedly exceed the required gas fill pressure, and the bar would repeatedly emerge from the housing such that the marking or markings would appear, which marking or markings would then at least intermittently indicate an adequate gas fill pressure. If this signal is interpreted incorrectly, an undershooting of the required gas fill pressure will not be noticed, and the percussive mechanism will consequently be operated with an excessively low gas fill pressure, resulting in a reduction in the performance of the percussive mechanism and the risk of damage to components.
Since the length to which the bar protrudes beyond the housing is dependent on the gas pressure and increases with increasing gas pressure up to a maximum structurally limited length, the user must measure the length or take notice of whether one or more markings present on the bar are visible. The reading of the indicator is thus cumbersome and requires knowledge regarding the interpretation of the length or of the markings.
An undershooting of the required fill pressure is not clearly indicated, because during operation of the percussive mechanism, when the percussive piston is situated above the rest position, an adequate gas fill pressure is indicated.